This invention relates to a unit for inspecting a surface which is for inspecting mainly a flaw made on an object to be inspected which has a specular surface such as a CD, a semiconductor wafer, a DVD, an MD or the like.
Conventionally, a variety of units for inspecting a surface are devised in order to inspect a flaw made on an object to be inspected which has a specular surface such as a CD, a semiconductor wafer or the like. As one of the units for inspecting a surface, the unit shown in FIG. 23 is already known in which light from a lighting unit having an area illuminant is irradiated uniformly on a surface of an object to be inspected so as to detect whether there is a flaw or rot by capturing an image of the reflected light.
However, in case a surface to be inspected is specular, if light which is not parallel such as diffused light irradiated from a plurality of light sources is irradiated on the surface, a flaw or a carved mark on the surface might not be detected, thereby to hinder an effective inspection on the surface. More concretely, as shown in FIG. 21, if a flaw is subtle such as a scratching linear flaw 92 or a point flaw 92, it is extremely difficult to detect the flaw.
In order to solve the above problems, a unit for inspecting a surface in accordance with this invention is so arranged that light irradiated from a point light source or close to a point light source is refracted by a lens so as to gradually converge in a condition of being close to parallel, the light is irradiated on a surface to be inspected and an image capturing means is arranged at a position where the reflected light converges.
More particularly, a unit for inspecting a surface is utilized in inspecting a flaw generated on a specular surface to be inspected or in reading a carved mark on a specular surface to be inspected and is characterized by that an illuminating means having a point illuminating element as a point light source or close to a point light source, a Fresnel lens, a half mirror and an image capturing means are supported by a body, wherein light is irradiated from the illuminating means, the light is refracted by the Fresnel lens so as to converge in a condition of being close to parallel, the refracted light is reflected by the half mirror, the light is irradiated on the specular surface to be inspected, the refracted light by the Fresnel lens is reflected against the half mirror, the reflected light is irradiated on generally whole area of the surface to be inspected and the reflected light is introduced into the image capturing means provided at a position where the light converges.
In accordance with the arrangement, clear light and shade contrast is shown between the portion where a flaw is formed and the other portion. This makes it possible to detect a subtle flaw such as a linear flaw or a point flaw which has not been able to be detected with conventional units for inspecting a surface. It is considered that this phenomenon is caused due to the following reasons.
When light having a converging characteristics is irradiated on a specular surface of an object to be inspected, a reflected image is introduced into an image capturing means in a condition that the image is gradually reduced as the light converges while the light irradiated on a portion where a flaw is formed reflects in a direction different from a converging direction due to subtle concave and convex of the flaw. As a result, it is considered that the light reflected from the portion where the flaw is formed does not reach the image capturing means, which makes the portion appear to be dark on the image captured by the image capturing means.
For an object whose surface to be inspected is relatively large such as a CD, a semiconductor wafer, a DVD or an MD, a length of an optical path is required to be lengthened quite a lot in order to make almost parallel light convergent, therefore it is difficult to make a size of the unit for inspecting a surface realistic. In order to effectively solve this problem, it is preferable that light reflected against a surface to be inspected is introduced into an image capturing means by reflecting the light a plurality of times against a plurality of reflecting mirrors provided inside a body of a unit. In addition, a thin, short in focal length and low-priced Fresnel lens makes a contribution on downsizing the unit and a low price.
For making an image captured by the image capturing means not to be upside down or not to be contrary in right and left to the actual object, it is preferable that an even number of the reflecting mirrors are provided.
In order to make it easy to adjust a position where an image is created or to adjust field of the image capturing means so as to deal with a change of an optical path length due to a difference of a position where an object to be inspected is placed, it is preferable that the image capturing means can be detachably mounted on outside the body of the unit, a refracting lens is arranged both on an optical axis of the light and near the image capturing means, and the refracting lens can be moved slidably along the optical axis, that the illuminating means is arranged to move along an optical axis of the light irradiated from the illuminating means, or that the image capturing means is arranged to move along the optical axis of the light introduced into the image capturing means.
As a concrete example of the embodiment, it is represented that the point illuminating element comprises a column-shaped optical Transmitting body having a light guiding face at one end thereof and an illuminating face at the other end thereof and a plurality of LEDs or photo fibers arranged so as to gather the irradiated light on the light guiding face of the column-shaped optical transmitting body, and is so arranged that the light is irradiated from the illuminating face wherein a light diffusing portion is provided on the illuminating face of the column-shaped optical transmitting body so that light diffusion effect is produced.
In order to inspect a surface satisfactorily it is preferable that a part or whole of the body is provided with a delustered processing.
Further, in order to make it possible to inspect not only a specular surface but also, for example, if a CD, a back of the specular surface such as a printed surface so as to improve general purpose properties of the unit, it is preferable that light is irradiated from an illuminating means provided near a focal point of a Fresnel lens, the light is refracted by the Fresnel lens so as to converge, the refracted light is reflected against a half mirror, the light is irradiated on generally whole area of a specular surface to be inspected and the reflected light is introduced into an image capturing means wherein the illuminating means comprises a point illuminating element as a point light source or close to a point light source and a ring-shaped area illuminating element arranged to surround the point illuminating element, and the point illuminating element and the area illuminating element are so arranged to be switched to illuminate.
More specifically, the point illuminating element is illuminated for inspecting a specular surface as mentioned above while the area illuminating element is illuminated for inspecting a printed surface or the like.
In accordance with the arrangement, other surfaces such as a printed surface besides a specular surface can be inspected by means of the area illuminating element. Especially with the unit, the light irradiated from the illuminating element is promoted to diffuse by passing through the Fresnel lens, thereby to improve accuracy of inspection. In this case, it is preferable that the light irradiated from the illuminating element is white and the image capturing unit can display in color.
As a concrete example of the area illuminating element, it is represented that comprising a disk-shaped transparent body, a disk-shaped supporting plate which is overlapped with one of the face plates of the transparent body and a plurality of LEDs arranged to surround the transparent body so as to illuminate light toward the center of the transparent body and provided with a through hole at the center thereof to pass through the light irradiated from the point illuminating element wherein the other face plate of the transparent body is made to area-illuminate the light as an illuminating face.
In accordance with the above-mentioned invention, clear light and shade contrast is shown between the portion where the flaw is formed and the other portion. This makes it possible to detect a linear flaw such as a scratch or a subtle flaw due to a bump trace which has not been able to be detected with conventional units for inspecting a surface and to read a carved mark.
In case this method is simply used, in order to deal with an object whose surface to be inspected is relatively large such as a CD or a DVD, a unit for inspecting a surface is likely to be large-sized and high-priced as mentioned above. However, if a lens used for making light parallel is a thin, short in focal length and low-priced Fresnel lens and light reflected against a surface to be inspected is introduced into an image capturing means by reflecting the light a plurality of times against a plurality of reflecting mirrors provided inside the unit, it is possible to realize a reasonable size and price for actual use.
If a number of a reflecting mirror provided is an even number, an image taken by the image capturing means can be made not to be upside down to the actual object or not to be contrary in right and left direction to the actual object.
If the image capturing means is detachably mounted in position on outside the body, a refracting lens is arranged on an optical axis of the light and near the image capturing means, and the refracting lens can be moved slidably along the optical axis, the illuminating means is provided to slidably move along an optical axis of the light irradiated from the illuminating means or the image capturing means is provided to slidably move along the optical axis of the light introduced from the illuminating means, it becomes possible to adjust a position where an image is created or to adjust view in flexibly cooperation with a change of an optical length due to difference of a position where an object to be inspected is set.
If the illuminating element comprises a column-shaped optical transmitting body having a light guiding face at one end thereof and an illuminating face at the other end thereof and a plurality of LEDs or photo fibers arranged so as to gather the irradiated light on the light guiding face of the column-shaped optical transmitting body, and is so arranged that the light is irradiated from the illuminating face and a light diffusing portion is provided on the illuminating face of the column-shaped optical transmitting body so that light diffusion effect is produced, part of the light irradiated on a portion where no flaw is made reflects so as not to converge because of a mounting error or distortion of the Fresnel lens or a subtle inclination or warp of the plate where a CD or DVD is placed. As a result, a portion where no flaw is made in an image shown on the image capturing means becomes a little dark, thereby to avoid a case that contrast between the portion where a flaw is made and other portion is blurred. This makes it possible to allow a mounting error or distortion of the Fresnel lens or a subtle inclination or warp of the plate where the object to be inspected is placed to a certain degree.
If a part or whole of the body of the unit is provided with a delustered processing, it is possible to conduct surface inspection satisfactorily.
If the illuminating means comprises a point illuminating element as a point light source or close to a point light source and a ring-shaped area illuminating element arranged to surround the point illuminating element and the point illuminating element and the area illuminating element are so arranged to be switched to illuminate, the point illuminating element can be illuminated for inspecting a specular surface as mentioned above while the area illuminating element can be illuminated for inspecting a printed surface or the like. As a result, other surfaces such as a printed surface besides a specular surface can also be inspected, thereby to improve general purpose properties of the unit. Especially with the unit, the light irradiated from the illuminating element is promoted to diffuse by passing through the Fresnel lens, thereby to improve accuracy of inspection.
If the area illuminating means comprises a disk-shaped transparent body, a disk-shaped supporting plate which is overlapped with one of the face plates of the transparent body and a plurality of LEDs arranged to surround the transparent body so as to illuminate light toward the center of the transparent body and is so arranged that a through hole is provided at the center thereof to pass through the light irradiated from the point illuminating element and the other face plate of the transparent body is made to area-illuminate the light as an illuminating face, it is possible to realize a preferable unit for inspecting a surface by making use of an LED""s characteristic of long life.